Frequency-modulated continuous-wave (FMCW) radar is a measuring radar that is capable of determining distance and/or relative speed. For example, in vehicles like cars and trucks, frequency-modulated continuous-wave radar systems are used to detect a distance to other objects and to measure a relative speed with respect to other vehicles. The output of such radar systems is used to generate warming signals for warning the driver and/or to automatically intervene in dangerous situations. In FMCW systems the transmitted signal (round a known stable frequency continuous wave) varies up (and down) in frequency over a fixed period of time-frequency modulation refers in this document to the varying of the frequency of the continuous wave. A chirp time is the length of the time interval in which the frequency increases (and decreases). Several types of frequency modulations are known in the field of FMCW radar. For example, in slow frequency modulation, the frequency of the transmitted continuous wave is modulated according to a triangular shaped wave and a chirp time is relatively long, for example, 10 milliseconds. In fast frequency modulation the frequency of the transmitted continuous wave is modulated according to a sawtooth wave and the chirp time is relatively short, for example, 100 microseconds. An effect of fast frequency modulation is that the beat frequency is increased while the Doppler frequency remains the same compared to the slow frequency modulation.
In published German patent application DE102008009596A1 a circuitry is disclosed for generating a frequency modulated continuous wave signal for a radar system that is frequency modulated according to a sawtooth-like waveform. However, the disclosed circuitry is not robust against external perturbations and variations.